【正文】 eaning for improving the const ruction quality of Shuibuya project .As a brandnew technology of modern spatial satellites navigation and position ing system,GPS has g radually replaced the normal optical and electrical surveying equipment in more and more fields. Since 1980s, especially after 1990s,GPS techno logy has lead the spatial positioning technology , bining with modern muni cation technology，to a revolutionary change. The method for simultaneously determ ineing three dimensional coordinates by GPS has changed the traditional positioning technology from land with inshore to entire ocean and outer space, from statics to kinematics, from point positioning to network difference, from afterwards processing to realtime positioning and navigation, and absolute and relative positioning pr233。cisi on ing to meter level, centimeter level, even submillimeter level, therefore, expands the fields of application and effect in every walk of life. The fast development and improvement of modern data munication technology, puter technology, electrical technology and the spatial positioning technology on behalf of GPS make supervision of high precision realtime continuity and automation feasible. According to the requirements o f construction quality management for roller paction in filling engineering, by means of the global satellite positioning technology, the wireless data munication technology, the puter technology and the data processing and analysis technology,and integrating with the roller p action machine, in 2004 Wuhan University and Qing jiang Hydroelectric Develop ment Corp. Ltd. Jointly developed a realtime supervisory system suitable for the quality management needs of roller pact ion in filling engineering, i. e. realtime supervisory system of filling construction quality( GPS system for short afterwards) . The system has prehensive functions of realtime, high precision, continuity, automation etc. , so can be applied to realtime supervising construct ion quality of filling paction for dam, road, protection dike, airport etc. and bees an effective assistant of ensuring the construction quality for project . Combining with engineering needs and system characteristics, the position, key techniques and schemes of the system are discussed in this paper. The height accuracy of the system is analyzed and the preliminary application is introduced.1 Composition and characteristics of GPS Realtime supervisory system1. 1 Composition of the systemHardware unit of the system mainly includes 3 parts as follows:1) Receiving system of GPS satellite signals。2) Wireless network data munication system。3) Computer system.Fig. 1 Illustration of the system network structure According to the requirements of paction for filling and ram ming engineering and construction quality management to system, the system is posed of supervisory center, network relay station, locale subcontrol station,GPS reference station and mobile terminals ( including roller paction machines and quality supervisor work ing vehicle) , regarding the effect of wireless munication from topographic environment. Fig . 1 is the illustration of construction quality supervisory system for filling paction project . If the topographic environment is good and the distance between the filling construction onthespot and the system supervisory center is not long, the network relay station can be removed.1. 1. 1 Supervisory center Supervisory center is the heart of the system,where the differential data of GPS reference station are emitted to the GPS mobile stations, and at the same time, receiv es the position information fed back by the mobile stations continuously and real timely through wireless data munication. Combining the needs of construction,electronic display screen equipped in the supervisory center can realtimely display the accurate moving location and status information of the roller paction machin es as well as the quality supervisor working vehicle for paction planes of the dam, remotely monitor the state of paction quality of filling engineering, and offer leaders the basis of decision. T he processing , analysis, storage of the system data and so on are carried out in the supervisory center.1. 1. 2 Locale subsupervisory stationLocale subsupervisory station is the extension of the system control center, and provides convenience for locale supervisor. By accessing information of the system supervisory center, the supervisor can master the status of engineering construction and the construction quality in time just in the construction locale supervisor quality deviation appears, the supervisor can tackle with the construction side on the construction locale, reminding the constructors and asking them for rectifying.1. 1. 3 GPS reference stationGPS reference station is set for increasing the supervisory precision of the system by means of DGPS technology. We set a GPS receiver on a known site as a reference station and carry out GPS observation, then emit the GPS observation data and known location information of the reference station realtimely to the GPS mobile stations, and process the data along with mobile stations39。 GPS observation data by means of diferential processing of carrier phases, consequently calculate the spatial location information of the mobile stations, whose positioning precision can increase. T he method above is named DGPS technology. In general, GPS reference station should be set up in the supervisory center for the sake of convenient supporting pow er, management and maintenance. To ensure the supervisory precision, it is stressed that the distance between the GPS reference station and the construction area must be less than 56 km, and the distance controlling requirement can be satisfied in practice.1. 1. 4 Mobile terminalMobile terminal includes systemrequiring equipments installed in the project supervisory car and ro